Leading climate scientists and advisors stand accused of giving the public false hope that dangerous levels of warming can be averted.

That’s the view of Oliver Geden, a researcher at the Berlin-based German Institute for International and Security Affairs.

Writing in the latest edition of Nature, Geden says government advisors are under pressure to offer solutions that can keep warming within what is deemed acceptable levels.

“Scientific advisers must resist pressures that undermine the integrity of climate science,” he writes.

“Instead of spreading false optimism, they must stand firm and defend their intellectual independence, findings and recommendations – no matter how politically unpalatable.”

He adds: “Scientific advisers should resist the temptation to be political entrepreneurs, peddling their advice by exaggerating how easy it is to transform the economy or deploy renewable technologies, for instance.”

In 2009, governments agreed to limit temperature rises to below 2C above pre industrial levels, although some countries especially vulnerable to climate impacts say this should be 1.5C.

The 2C goal is viewed as politically delicate. When US climate envoy Todd Stern argued it was impractical in 2012 he was met with stiff criticism from developed and developing countries.

Tipping point

But while some believe it will be hard to achieve, scientists say passing that limit will lead to more floods, droughts, and sea level rise due to melting ice sheets.

In March this year Petra Tschakert, a coordinating lead author of the Intergovernmental Panel on Climate Change’s latest assessment said it was “utterly inadequate”.

In June, the UN is due to report on a review of the 2C goal, but with negotiations on a global climate pact at an advanced stage and due to be signed off at a Paris summit in December, Geden argued it is time for a reality check on those proposed targets.

Specifically he maintained the reliance on negative emissions in some potential climate mitigation trajectories is impractical.

“Most models assume that this can be achieved using a combination of approaches known as BECCS: bioenergy (which would require 500 million hectares of land — 1.5 times the size of India) and carbon capture and storage, an unproven technology.”

And he said talks in Paris later this year world likely be aimed at a “weaker climate goal” if policymakers read the “fine print” in reports produced by the UN’s IPCC climate science panel, which he says are less confident about avoiding 2C.

Policy neutral

The IPCC has historically steered clear of policy pronouncements, instead offering a range of warming scenarios and emission trajectories to allow governments to formulate policy.

Its last set of reports, issued between 2013 and 2014, warned if countries continues to burn fossil fuels at their current rate the world could lock in 2C of warming in under 30 years’ time.

Speaking to RTCC, Geden said he was in favour of ambitious climate policies, but he wanted to highlight what he felt were misleading benchmarks.

“There is an uneasiness among climate scientists… it will be a polarised discussion,” he said, “but I don’t want to lose the silent majority of climate scientists.”

Commenting on the paper, Niklas Höhne, director of the New Climate Institute said Geden had confused climate science and politics in his argument.

“The IPCC has never advocated for any target and has not commented on the feasibility, nor has the UNEP gap report. Both have shown the scenarios and the related assumptions, such as the need for net negative global emissions in some cases,” he said.

“Both reports do not make a judgement on the feasibility. They leave that to the policy makers.”

Höhne – an IPCC lead author on climate policies and international cooperation – said there was a “political value” in having a target for countries to aim for.

“The value 2C, 2.5C or 1.5C and its feasibility can be contested and remains a value judgement, but it is important to have one at all.

“Since Geden does not present an alternative, he can be read that he wants to abandon a goal altogether. This would leave us with a far less climate friendly political situation than before, as negotiating a new goal would take years.”

In a statement Nick Nuttall, spokesperson for the UN’s climate body, argued the 2C goal should be seen less as a target and more as a “defence line” for humanity.

“Every country on Earth–supported by rising ambition by thousands of cities and companies– is working with increasing optimism towards a new universal agreement in Paris in December,” he said.

“As we have said many times, the climate action plans or INDCs being put forward so far will not on their own keep the world under a 2 degrees C rise.

“But we are confident that Paris can put in place the policies, pathways, structures and finance that can assist all nations to progressively ramp up their ambition over time in order to make the transformations needed to stay under the internationally agreed goal.”